The Poser UI is a great example of how NOT to do things. I've had the P4 ProPack trial (uninstalled it ages ago), P5, P6 and now P7. In all versions the UI is horrible.

As for functionality, P7 works the best for me. I often use dynamic cloth, sometimes dynamic hair. P5 introduced them, P6 fixed them, and they also work fine in P7. I still miss some features though.
The render engine in P7 is a step up from P6, and P6 is a step up from P5. Firefly is a decent render engine, although it has its quirks. Anyway, most of my scenes refuse to render in the old P4 renderer, but do render in Firefly.

I would NEVER go back to P4. It misses far too many features that I use everyday.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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